Custom tooled printed circuit board

ABSTRACT

A printed circuit board contains a plurality of component contacts for receipt of electronic components and a plurality of electrically conductive traces, each trace being electrically connected to a corresponding one of the component contacts. A corresponding plurality of interconnect holes is formed on a selected portion of the printed circuit board with each interconnect hole contacting uniquely a corresponding one of the plurality of electrically conductive traces. A multiplicity of custom conductive traces are then formed in the interconnect region such that each of the multiplicity of conductive traces interconnects at least one of the interconnect holes to at least one other interconnect hole thereby to form an electrically conductive path between each of the interconnect holes interconnected by the custom conductive traces. A user is thus able to achieve a desired electrical function from the electronic components to be connected to the printed circuit board.

This application is a division of application Ser. No. 07/466,153, filedJan. 17, 1990.

FIELD OF THE INVENTION

This invention relates to printed circuit boards and in particular to aprinted circuit board which is custom programmable by the designer of anelectronic system so as to implement a desired function typically,though not necessarily, using a field programmable printed circuit boardof the type described in copending U.S. Pat. Application Ser. No.07/410,194 filed Sep. 20, 1989 by Amr M. Mohsen and entitled "FieldProgrammable Printed Circuit Board".

BACKGROUND OF THE INVENTION

Printed circuit boards are commonly used in electronic devices such asinstruments, computers, telecommunication equipment and consumerelectronic products. Typically, an engineer will design a printedcircuit board to carry the types of components necessary to implementthe desired electronic function and to fit in the space available forthe board. Consequently, each printed circuit board typically is customdesigned. To design a custom printed circuit board is expensive, takestime and requires the fabrication of prototype printed circuit boards.If errors are found in the prototypes, then the printed circuit boardmust be redesigned. Such a process often delays the planned introductionof a new product.

To alleviate this problem I invented a field programmable printedcircuit board which is described in my above referenced copending patentapplication. In accordance with my invention described in the abovereferenced application, I provide a printed circuit board of uniqueconfiguration combined with one or more special programmable integratedcircuit chips (hereinafter called "programmable interconnect chips" or"PICs") to provide a user programmable printed circuit board capable ofbeing used to provide any one of a plurality of functions. As describedin the above referenced application, in one embodiment of thatinvention, a field programmable printed circuit board comprises:

(1) a multiplicity of component contacts for receipt of the leads ofelectronic components;

(2) a corresponding multiplicity of PIC contacts for receipt of theleads on the package or packages of the programmable interconnect chipor chips; and

(3) one or more layers of conductive traces, each conductive traceuniquely connecting one component contact to one PIC contact.

Typically, electronic components comprise integrated circuits and/ordiscrete devices contained, respectively, in standard integrated circuitor discrete device packages and in addition, discrete elements whichinclude resistors, capacitors and inductors, for example. As describedin the above-mentioned application, each PIC contact brings acorresponding trace from a selected level on the PC board to the surfaceof the PC board so that trace is then connectable to a pin or electricalcontact on a programmable interconnect chip. For every componentcontact, (the function of which is to receive the pin or electricalcontact of an electronic component,) there is a correspondingelectrically conductive trace which interconnects that component contactto a corresponding PIC contact (the function of which is to receive andelectrically contact the pin or electrical contact of the programmableinterconnect chip) in the printed circuit board. Thus, each componentcontact is electrically and uniquely connected to a corresponding PICcontact.

For printed circuit boards to be produced in high volume it is desirableto reduce the number of integrated circuit chips to be placed on theprinted circuit board.

SUMMARY OF THE INVENTION

In accordance with this invention a custom tooled printed circuit boardis provided that has the electrical characteristics substantiallysimilar to the electrical characteristics of the field programmableprinted circuit board described in the above-referenced applicationwithout the use of the programmable interconnect chip.

As an advantage of this invention, engineers who first implement theirsystem design with the field programmable printed circuit board forprototype and debugging purposes are able to implement their design inhigh volume and at low cost without the need to re-engineer new customtooled printed circuit board. The avoidance of the redesign of a newcustom tooled PC board eliminates two to three months of time and savesa substantial engineering effort and thus the comparable cost associatedwith this effort. Thus an engineer who employs the field programmableprinted circuit board described in the above-referenced application toimplement his system is able, using this invention, to obtain a customtooled printed circuit board at a low cost with approximately the sameelectrical characteristics as the field programmable printed circuitboard.

In accordance with this invention, the field programmable PCB of myinvention described in the above-mentioned application contains twoareas, one containing component holes and the other containing PICholes. The PIC holes are typically on a small portion of the surface ofthe printed circuit board. In accordance with this invention, the areacontaining the PIC holes is enlarged slightly so as to be capable ofreceiving traces to allow connection between any two or more PIC holes(also sometimes called "PIC vias" or "PIC pads ") in the PIC orinterface area. All of the layers of traces used to connect componentholes to PIC holes in the field programmable PCB are used in the customtooled PCB of this invention together with one additional trace layer.This additional trace layer allows the interconnection of selected PICvias or PIC pads at the edge of the PIC area or interface area or whenit is otherwise impossible to connect two PIC holes, PIC vias or PICpads using traces on the PC board layers containing conductive tracesconnecting component holes to PIC holes, PIC vias or PIC pads.

This invention will be more fully understood in conjunction with thefollowing detailed description taken together with the followingdrawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the trace architecture for the field programmable PCBin the area of the PIC holes in accordance with the field programmableprinted circuit board described in my copending Application Ser. No.07/410,194.

FIG. 2 illustrates the custom tooled printed circuit board of thisinvention to connect two nodes on the printed circuit board directly.

FIG. 3 illustrates an isometric, cutaway view of the PIC area (alsocalled TMP interface area) configured to a custom configuration by thecustom interconnections of this invention.

DETAILED DESCRIPTION

The following description is meant to be illustrative only and notlimiting. Other embodiments of this invention will be obvious to thoseskilled in the art in view of this description.

The field programmable printed circuit board upon which this inventionis based is described in detail in the above-mentioned U.S. Pat.Application Ser. No. 07/410,194 hereinafter the "'194 application"). The'194 application in its entirety is hereby incorporated by referenceinto this application.

As shown in FIG. 1, the traces 103-r,c from the component holes 102-r,cin FIG. 1a of the '194 application (holes 102-r,c are not shown in theFigures of this application) are brought on their respective layers101-1 through 101-L, where L is the maximum number of layers, to theregion of the printed circuit board containing the PIC holes 104-1,1through 104-R,C. R is the total number of rows of component holes 102 onthe printed circuit board and C is the total number of columns ofcomponent holes 102 on the printed circuit board, r is given by 1≦r≦Rand c is given by 1≦c≦C. As stated in the above-referenced '194application, each component hole 102-r,c has a uniquely correspondingPIC hole 104-r,c and is connected thereto by a conductive trace 103-r,c.A programmable interconnect chip 105 (shown in FIG. 1a of the '194application) makes electrical contact with each PIC hole 104-r,c. Theprogrammable interconnect chip 105 then is configured by the user, asdiscussed in the '194 application, to interconnect selected componentholes 102-r,c by means of the proper configuration of the switchingelements on the programmable interconnect chip 105. FIG. 1 illustrates aportion of the interface area of the field programmable printed circuitboard containing a number of PIC holes 104-r,c arranged to receive aprogrammable interconnect chip. Of importance, the leads or conductivetraces 103-r,c run for the most part in the y direction. No leads103-r,c run a substantial distance in the x direction. Moreover, theleads 103-r,c on the first layer 101-1 of the printed circuit boardcontact the PIC holes 104-r,c in the first few rows (for example, thePIC holes 104-l,x through 104-4,x in rows one through four) while theleads 103-r,c on the second layer 101-2 of the printed circuit boardcontact the PIC holes 103-r,c in a few of the following rows (forexample, PIC holes 104-5,x through 104-8,x in rows five through eight).Accordingly, the PC board can be custom designed by adding one morelayer 101-(L+1) of PC board material to allow conductive traces to beformed thereon to interconnect two PIC holes 104 which otherwise couldnot be connected with conductive traces on PC board layers 101-1 through101-L. This additional layer 101-(L+1) allows a custom designed seriesof traces to be placed in the interface area of the PCB board.

In general, a particular PIC hole is connected to a component hole by atrace formed on a selected layer of the PC board Therefore, any PIC holecan be connected to any other PIC hole in general by forming aninterconnection trace on those layers of the PC board not containingtraces contacting the two PIC holes to be interconnected. The additionallayer for the placement of traces gives added flexibility to thedesigner to allow the interconnection of two PIC holes which otherwisewould not be able to be interconnected because of previously existingtraces on the other PC board layers.

FIG. 2 illustrates such an interconnection. As shown in FIG. 2, the PICholes 104 are spaced apart slightly further than in FIG. 1 to allow roomfor traces which travel predominantly in the x direction across the PCBto interconnect to PIC holes 104 thereby to eliminate the programmableinterconnect chip 105 described in my above referenced copendingapplication. As illustrated in FIG. 2, PIC hole 104-6,1 is connected bytrace 106-1 to PIC hole 104-4,3. PIC hole 104-6,1 is connected to itscomponent hole 102-6,1 (not shown in FIGS. 1, 2 and 3) by a conductivetrace 103-6,1 on the second layer 101-2 of PC board material whilecomponent hole 104-4,3 is connected to its corresponding component hole102-4,3 (also not shown in FIGS. 1, 2 and 3) by a conductive trace103-4,3 (not shown in FIG. 2) on the first layer 101-1 of PCB boardmaterial. Because no conductive traces 103-r,c from component holes102-r,c to PIC holes 104-r,c are formed on the first layer 101-1 of PCBboard material beyond row 4, trace 106-1 can be formed on the firstlayer 101-1 of PCB board material.

Next PIC hole 104-7,1 which is connected to its corresponding componenthole 102-7,1 by a conductive trace 103-7,1 on the second layer 101-2 ofPCB material is connected by trace 106-2 to PIC hole 104-5,4. PIC hole104-5,4 is connected to its corresponding component hole 102-5,4 (shownin the '194 application) by a conductive trace 103-5,4 (not shown inFIG. 2) on the second layer 101-2 of PC board material. Because none ofthe conductive traces 103-r,c on the first layer 101-1 of PCB boardmaterial extend beyond row 4 of PIC holes 104 and because conductivetrace 106-1 does not cross the proposed path of conductive trace 106-2,conductive trace 106-2 can also be formed on the first layer 101-1 of PCboard material. Should, however, PIC hole 104-7,1 be required to beconnected to PIC hole 104-5,2, the first layer 101-1 of PC boardmaterial can also be used but the conductive trace would then follow thedashed line 106-3 as shown. Should it not be possible to interconnecttwo PIC holes 104 on the already existing layers of PC board material,an additional layer 101-(L+1) of PC board material is added on which noconductive traces are formed connecting component holes to correspondingPIC holes. This conductive layer 101-(L+1) provides additionalinterconnect flexibility to the design of the custom PC board inaccordance with this invention. This additional layer 101-(L+1) can beplaced on the bottom, on the top or in between any two of the PC boardlayers 101 already formed on the PC board.

The architecture of the traces 106 illustrated in FIG. 2 allows the samelength trace, the same loading capacitance and the same cross-couplingon the custom tooled printed circuit board in accordance with thisinvention as on the field programmable printed circuit board describedin my above-referenced copending application. The track length of theprinted circuit board conductive traces 103 will increase slightly inthe interface area (that is, the area where formerly the programmableinterconnect chip 105 was placed) because the space between the PICholes 104 is increased slightly to accommodate the interconnectiontracks 106.

The tracks 106 which interconnect selected PIC holes 104 will addcapacitance comparable to the programmable interconnect chip 105capacitance. The resistance of the interconnects on the programmableinterconnect chip 105 (sometimes called programmable interconnectsubstrate or "PIS") will be larger than on the custom tooled printedcircuit board of this invention. However, through the use of simulationsoftware to simulate various interconnection schemes, the impact of theresistance on the connection delays can be simulated and the circuitproperly configured. Typically, the effect of this resistance on delayis a fraction of the total delay in the circuit.

One of the features of this invention is that the standard programmableprinted circuit board described in the above-mentioned U.S. patentapplication is modified by custom programming interconnections in theinterface area of the PC board. The interface area comprises thatportion of the field programmable PC board above which the programmableinterconnect chip or chips are placed. In accordance with thisinvention, the programmable interconnect chip is replaced by traces 106formed to interconnect the various traces 103 from the component holes102 on the field programmable printed circuit board into the desiredconfiguration to yield the desired system and function. The interfacearea contains the "via holes" which are used to interconnect traces ondifferent layers of the PC board to form the desired circuit. Theportion of the printed circuit board containing the component holes 102is unaltered by the formation of the custom traces 106 in the interfacearea of the PC board. The custom traces are formed using standardprinted circuit board fabrication techniques. The advantage of thisinvention however is that the custom traces 106 are formed over a muchsmaller portion of the printed circuit board thereby reducingsubstantially the engineering costs associated with the fabrication ofthe custom portion of the PC board In addition, the turn-around time issubstantially reduced because the operation of the circuit can first beverified using the field programmable printed circuit board of theabove-referenced application with the result that engineering time andeffort are substantially reduced.

While the invention has been described as utilizing one additional layer101-(L+1) on the printed circuit board, of course, more than oneadditional layer can be used, if desired, to improve the flexibility ofinterconnection and to reduce the additional area increase of theinterface when the programmable interconnect chip is replaced with thecustom interconnects 106 of this invention.

The custom traces 106 formed in the interface area of the fieldprogrammable printed circuit board to convert this printed circuit boardto a custom programmable printed circuit board are defined usingcomputer aided design tools including algorithms of a type well known inthe art.

FIG. 3 illustrates in isometric view the conductive traces 106 of thisinvention formed in the interface area of the programmable printedcircuit board to interconnect selected vias or holes 104 in accordancewith the required circuit configuration. Note that conductive traces 106can interconnect a PIC hole 104 directly to a conductive trace 103 or toanother conductive trace 106 depending upon the requirements of thecircuit. Thus conductive trace 106-7 interconnects PIC hole 104-1,10 toconductive trace 106-8 which in turn interconnects conductive holes104-3,10 and 104-2,6.

Other embodiments of this invention will be apparent to those skilled inthe art in view of the above disclosure.

I claim:
 1. Structure comprising:a printed circuit board containing afirst region and an interface area; a plurality of component contactsformed in said first region of said printed circuit board for receipt ofelectronic components; a plurality of electrically conductive tracesformed on said printed circuit board, each trace being electricallyconnected to a corresponding one of said component contacts; acorresponding plurality of interconnect contacts formed in saidinterface area of said printed circuit board, each interconnect contactbeing connected uniquely to a corresponding one of said componentcontacts by one of said plurality of electrically conductive traces; anda multiplicity of custom conductive traces formed on said printedcircuit board in said interface area, each of said custom conductivetraces interconnecting at least two of said interconnect contactsthereby to form an electrically conductive path between said at leasttwo interconnect contacts.
 2. Structure as in claim 1 wherein saidcomponent contacts comprise holes formed through said printed circuitboard, each of said holes being plated with a conductive material. 3.Structure as in claim 2 wherein said interconnect contacts compriseholes formed through said printed circuit board, each of said holesbeing coated on its interior surface with a conductive material. 4.Structure as in claim 1 wherein said printed circuit board contains atleast two layers of insulating material, each of said two layerscontaining thereon a subset of said plurality of electrically conductivetraces.
 5. Structure as in claim 1 wherein said printed circuit boardincludes at least one additional layer of insulating material containingnone of said plurality of electrically conductive traces, said at leastone additional layer being suitable for containing one or more of saidmultiplicity of custom conductive traces formed on said printed circuitboard in said interface area.